A long term evolution (LTE) system of 3GPP organization for standardization supports two duplex modes: a frequency division duplex (FDD) mode and a time division duplex (TDD) mode. As shown in FIG. 1, FIG. 1 is a schematic diagram illustrating a FDD wireless frame structure in a prior art. In a FDD system, a length of each wireless frame is 10 ms, and the wireless frame includes 10 subframes, each of which has a length of 1 ms. The subframe is composed of two consecutive time slots, each of which has a length of 0.5 ms, that is, the kth subframe includes time slot 2k and time slot 2k+1, wherein k=0, 1, . . . , 9, As shown in FIG. 2, FIG. 2 is a schematic diagram illustrating a TDD wireless frame structure in the prior art. In a TDD system, each wireless frame having a length of 10 ms is divided into two half frames, each of which has a length of 5 ms. Each half frame includes 3 special fields and 8 time slots, each of which has a length of 0.5 ms. The 3 special fields, of which the sum length is 1 ms, are respectively a downlink pilot time slot (DwPTS), a guard period (GP) and an uplink pilot time slot (UpPTS). Each subframe is composed of two consecutive time slots, each of which has a length of 0.5 ms, that is, the kth subframe includes time slot 2k and time slot 2k+1, wherein k=0, 1, . . . , 9. A downlink transmission time interval (TTI) is defined on a subframe.
When a TDD wireless frame is configured, seven kinds of uplink and downlink configurations are supported. As shown in Table 1, here, D denotes a downlink subframe, U denotes an uplink subframe, and S denotes a special subframe including the above 3 special fields.
Table 1
TABLE 1configuration transition serialpointsubframe numbernumberperiod01234567890 5 msDSUUUDSUUU1 5 msDSUUDDSUUD2 5 msDSUDDDSUDD310 msDSUUUDDDDD410 msDSUUDDDDDD510 msDSUDDDDDDD610 msDSUUUDSUUD
The first n orthogonal frequency division multiplexing (OFDM) symbol(s) may be used to transmit downlink control information that includes a physical downlink control channel (PDCCH) as well as other control information, wherein the n is equal to 0, 1, 2, 3, or 4. Remaining OFDM symbol(s) may be used to transmit a physical downlink shared channel (PDSCH) or an enhanced PDCCH (EPDCCH). In a LTE system, the PDCCH and the EPDCCH, called a downlink grant (DL Grant) and an uplink grant (UL Grant) respectively, carry downlink control information (DCI) for allocating an uplink channel resource or a downlink control resource. In the LTE system, DCI of different user equipments (UEs) are sent independently, so do the DL Grant and the UL Grant thereof.
In a LTE enhanced system, a larger operation bandwidth is obtained by composing multiple component carriers (CCs), i.e., a downlink link and an uplink link of a communication system are constituted by using carrier aggregation, so as to support higher transmission rate. Here, CCs that are aggregated together may adopt a same duplex mode (i.e., there are all FDD cells or all TDD cells), or may adopt different duplex modes (both the FDD cell and the TDD cell are existed). A base station may configure one UE to work in multiple cells, and one of them is called a primary cell (Pcell), while the other cell(s) is called secondary cell (Scell). For a LTE CA system, transmission of a hybrid automatic repeat request-ACK (HARQ-ACK) and channel state information (CSI) based on a physical uplink control channel is merely performed on the Pcell.
The LTE system mentioned above generally deployed in a licensed band, which may avoid interference of other system. Besides the licensed band, there is an unlicensed band. The unlicensed band has been allocated for other use such as a radar system and/or a wireless local area network (WiFi) system of the 802.11 family. The WiFi system of the 802.11 family works based on a mechanism of carrier sense multiple access/collision avoidance (CSMA/CA). A mobile station (STA) needs to detect a wireless channel before sending a signal. The wireless channel can be occupied to send the signal only if the wireless channel is in an idle state and remains in this state for a certain amount of time. The STA may judge the state of the wireless channel jointly by adopting a combination of two mechanisms. In one aspect, the STA may practically detect the wireless channel by adopting a carrier sensing technology. When a signal of other STA is detected or a detected signal power exceeds a preset threshold, it is affirmed that the wireless channel is busy. At this point, a clear channel assessment (CCA) which is reported by a physical layer module in the STA to its high level module indicates that the wireless channel is busy. In another aspect, the WiFi system of the 802.11 family also introduces a virtual carrier sensing technology, i.e., network allocation vector (NAV). A duration domain is included in each 802.11 frame. It affirms the period that cannot transmit any signal on the wireless channel by a NAV value that is set based on the duration domain. The NAV is to indicate a required reserve time of the wireless channel.
For the LTE system, to satisfy a requirement of increasing amount of mobile communication traffic, more frequency spectrum resource needs to be exploited. A possible solution is to deploy the LTE system on the unlicensed band. Because the unlicensed band has been allocated for other use, when the LTE system is deployed on the unlicensed band, its interference level is uncertain, so that it is generally difficult to guarantee quality of service for transmitting data in the LTE system. However, the unlicensed band may also be used for data transmission which requires lower QoS. In such a case, how to avoid interference of LTE system in the unlicensed band has become a problem needed to be solved urgently.